Heaters are used in petrochemical installations to heat fluids for a variety of purposes, typically to break apart larger hydrocarbon molecules into smaller molecules. The heaters contain tubes, up to and even more than a kilometer long, that pass first through a convection section of a heater then through a radiant section. During use, the heater tubes gradually become contaminated on their insides. This contamination, typically coke, tends to degrade the efficiency of the heater over time, which can lead to economic loss and can eventually cause the heater to stop working.
Various methods are known for decoking heaters. Coke is often removed by mechanical means, which requires a system shut down. Many pig designs cannot operate without significant disturbance to heater operation or are unable to withstand high temperatures of up to 500 C and, in some cases, up to 900 C in heater pipes. Some pig designs are inflexible and so are unable to accommodate small changes in pipe diameter and unable to traverse through 180-degree bends. Most pigging designs are too heavy or result in a significant pressure drop in the heater making their use during heater operation undesirable. Also, many pig designs fail to consider the change in fluid velocity as the pig passes through the heat exchanger. Many materials used for pig designs have temperature limitations or high densities, which make the designs unmanageable during heater operation.